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首页> 外文期刊>Biochemistry >Strength of Axial Water Ligation in Substrate-Free Cytochrome P450s Is Isoform Dependent
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Strength of Axial Water Ligation in Substrate-Free Cytochrome P450s Is Isoform Dependent

机译：无底物的细胞色素P450的轴向水连接强度取决于同工型。

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The heme-containing cytochrome P450s exhibit isoform-dependent ferric spin equilibria in the resting state and differential substrate-dependent spin equilibria. The basis for these differences is not well understood. Here, magnetic circular dichroism (MCD) reveals significant differences in the resting low spin ligand field of CYPs 3A4, 2E1, 2C9, 125A1, and 51B1, which indicates differences in the strength of axial water ligation to the heme. The near-infrared bands that specifically correspond to charge-transfer porphyrin-to-metal transitions span a range of energies of nearly 2 kcal/mol. In addition, the experimentally determined MCD bands are not entirely in agreement with the expected MCD energies calculated from electron paramagnetic resonance parameters, thus emphasizing the need for the experimental data. MCD marker bands of the high spin heme between 500 and 680 nm were also measured and suggest only a narrow range of energies for this ensemble of high spin Cys(S~?) → Fe~(3+) transitions among these isoforms. The differences in axial ligand energies between CYP isoforms of the low spin states likely contribute to the energetics of substrate-dependent spin state perturbation. However, these ligand field energies do not correlate with the fraction of high spin vs low spin in the resting state enzyme, suggestive of differences in water access to the heme or isoform-dependent differences in the substrate-free high spin states as well.
机译：含血红素的细胞色素P450在静止状态下表现出同工型依赖性铁自旋平衡，而在不同底物上具有依赖性的自旋平衡。这些差异的基础还不太清楚。在此，磁性圆二色性（MCD）在CYP 3A4、2E1、2C9、125A1和51B1的静止低自旋配体场中显示出显着差异，这表明轴向水与血红素连接的强度不同。特别对应于电荷转移卟啉到金属的跃迁的近红外谱带的能量范围接近2 kcal / mol。此外，实验确定的MCD频带与从电子顺磁共振参数计算出的预期MCD能量并不完全一致，因此强调了对实验数据的需求。还测量了在500至680 nm之间的高自旋血红素的MCD标记带，对于这些同工型之间的高自旋Cys（S〜？）→Fe〜（3+）跃迁的集合，仅显示了很窄的能量范围。低自旋态的CYP亚型之间的轴向配体能的差异可能有助于依赖于底物的自旋态扰动的能量。但是，这些配体场能与静止态酶中高自旋与低自旋的比例不相关，这暗示了在无底物的高自旋态中水获得血红素的途径差异或同工型依赖性差异。

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